1. Field of the Invention
The present invention pertains to a drive device for a continuous belt used in image forming apparatuses such as copying machines, printers, facsimile machines, and machines combining any of these functions.
2. Description of the Related Art
Apparatuses that form images on a sheet, such as copying machines, printers and facsimile machines, conventionally are equipped with mechanisms to rotate a continuous belt at various locations inside the apparatus. The continuous belts used in conjunction with such mechanisms include, for example, a transfer medium conveyance belt, a photoreceptor belt and an intermediate transfer belt.
A high degree of parallelism is required of the multiple rollers over which the belt is suspended and which cause the belt to rotate. If the rollers are not parallel, the belt shifts along the axes of the rollers and meanders as it rotates, resulting not only in poor quality images exhibiting mismatched color images, for example, but also in damage to the belt itself in some cases. One well known type of belt has parallel elastic guide members located at either edge of the bottom side of the belt in order to minimize the need for the rollers to be precisely parallel. In this type of belt drive device, belt shifting may be prevented by hooking the elastic guide members onto the end areas of the rollers.
However, the coefficient of friction between the elastic guide member and the roller end area is usually high, at 0.3 or more. Therefore, a meandering force is generated in the belt, and the elastic guide member is pushed out along the radius of the roller where the elastic guide member and the roller end area are in contact with each other. Consequently, the elastic guide member rides up on the roller, resulting in meandering of the belt and ultimately damage to the belt.
In order to reduce the friction between the elastic guide member and the roller end area, a belt drive device has been proposed in which the coefficient of friction between the elastic guide member and the roller end area is reduced by means of a coating (Japanese Laid-Open Patent Application Hei 6-51578).
However, the coating for this belt drive device is expensive. Moreover, the elastic guide members warp around the rollers, giving rise to the problems that the coating comes off easily and the life of the coating is short.